1. Field of the Invention
This invention relates to bonded non-woven fabrics and, more particularly, to a process for producing bonded non-woven fabrics. The bonded non-woven fabrics are useful in the production of articles of either flat or three-dimensional shape, including durable or permanent non-woven fabrics and non-durable or disposable non-woven fabrics. Examples of durable non-woven fabrics include those which are useful in producing home furnishings and furniture upholstery, such as placemats, tablecloths, bedspring covers, mattress covers, and drapery headers; those which are useful in producing automotive interiors; surgical garments and inner-linings of clothing garments; and other uses such as clothing tags, flags and banners, wall coverings, dust filter bags, and electrical insulation. Examples of non-durable fabrics include those which are useful in producing disposable diaper covercloths, wet-wipes, sheets, sanitary napkins, surgical dressings, and hospital draperies; and disposable specialty garments such as surgical gowns and hospital gowns.
2. Description of the Prior Art
As part of the increasing attention being given to health and environmental and industrial working conditions, greater attention is being paid to the components of sanitary and health care fabric products such as diapers, sanitary napkins, hospital drapes, disposable sheets and bed pans, and to the components of home furnishing, automotive, and clothing garment products with which persons come into contact. Non-woven fabrics for these applications are required to have an adequate tensile strength and abrasion resistance when wetted by water or aqueous systems such as body fluids (e.g. perspiration, etc.) and laundering systems. Generally the binders in current use for non-woven webs are crosslinked in order to obtain an adequate level of strength and abrasion resistance of the water-wet fabric. The crosslinking is normally based on formaldehyde, usually in the form of methylolated acrylamide although aminoplast crosslinkers are also used. Such systems are disclosed in the following two patents.
In U.S. Pat. No. 2,931,749, Kine et al. disclose non-woven fabrics of fibers bonded by a water-insoluble emulsion copolymer containing units of a compound from the group of acrylic acid, methacrylic acid, itaconic acid, and salts thereof with at least one C.sub.1 to C.sub.12 alkyl ester of acrylic and methacrylic acid, the copolymer being crosslinked to an insoluble condition by exposure to heat.
In U.S. Pat. No. 3,157,562, Kine et al. disclose, as a coating or impregnating composition, an aqueous dispersion of a water-insoluble linear addition polymer of N-methylolamide of (meth)acrylic acid, (meth)acrylamide, and at least one member of the group of acrylonitrile, styrene, vinyl toluene, vinyl acetate and C.sub.1 -C.sub.18 alkyl (meth)acrylates. Also, a non-woven fabric of fibrous material and a water-insoluble linear addition copolymer containing the N-methylolamide of (meth)acrylic and (meth)acrylamide, and a process for making the same, are disclosed.
Formaldehyde is known to be a skin irritant. There is recent evidence that it is mutagenic (W. D. N. Kaplan, Science, 108, 43 (1948)) and concern has also been expressed that it may be found to be carcinogenic. For similar reasons, other relatively hazardous components in addition to those which evolve formaldehyde (e.g., N-methylol acrylamide), such as acrylamide and acrylonitrile, are also to be avoided in the manufacture of polymers for use as binders for non-woven fabrics intended for the uses described herein and related uses.
Non-crosslinking systems have been taught as binders for non-woven fabrics for certain specialty applications. In U.S. Pat. No. 3,554,788, Fechillas discloses a water-sensitive disposable, i.e., dispersible in water and flushable in home water closets, fabric for similar sanitary and health product uses. The binder of the patent comprises from about 70 to 90% of a water-insoluble, substantially water-insensitive, film-forming, non-self-crosslinking polymer and about 10 to 30% of a water-soluble polymer. The water-soluble polymers are described as water-sensitive binders such as hydroxyethyl cellulose, carboxymethyl cellulose, natural gums such as guar and preferably the alginates, such as sodium alginate, having a psuedo-plastic flow properties.
In U.S. Pat. No. 3,616,166, Kelley discloses a non-woven fabric bonded by a blend of a linear polymer of ethyl acrylate having a minimum film temperature not above room temperature and a viscosity average molecular weight of about 150,000 to 300,000 and a hard polymer having a minimum film temperature of at least about 50.degree. C. in the ratio of 60 to 90% of the former and 40 to 10% of the latter. This material is used to make a heat sealable fabric.
In TAPPI, 59, 98-100 (1976), H. Chu et al. disclose radiation-curable systems of a polyester fiberfill web and a radiation-curable binder, namely a polyester-based acrylourethane and an epoxidized unsaturated oil capped with acrylic groups.
H. W. Rauhut, Adhesives Age, 12 (12), 28-34 (1969), discloses the use of ultraviolet pre-irradiation to improve adhesion of polyethylene to itself or to other materials in the presence of suitable adhesives and photosensitizers.
In U.S. Pat. No. 3,121,070, H. W. Coover, Jr. et al. disclose a process for "tailoring" polypropylene by thermally degrading polymers such as polystyrene, polymethylmethacrylate, and polymethylenediethylmalonate in the presence of polypropylene, blocks of the former polymers becoming chemically attached to polypropylene chains with only a relatively small amount of monomer being formed in the process.
In U.S. Pat. No. 3,878,019, Chapman et al. disclose a process for producing a bonded non-woven web by forming a non-woven web of fibrous material, applying on the web a film-forming polymer containing a photosensitive group therein or adding thereto a compound containing a photosensitive group, subjecting discrete locations of the polymer-coated web to UV light to cause cross-polymerization of the polymer at the discrete locations to effect polymer bonding of the web at these locations, and removing unpolymerized polymer from the web.
In copending U.S. Ser. No. 793,656, filed May 9, 1977, now U.S. Pat. No. 4,148,987 issued Apr. 10, 1979, assigned to the same assignee to which the present application is assigned, Winey discloses monoethylenically unsaturated derivatives of substituted benzophenones and acetylphenones and linear addition copolymers thereof which crosslink on exposure to UV light. The linear addition copolymers are useful as binders for non-woven fabrics including disposable diapers, the binder-impregnated fabrics being curable by UV light to render the product fabrics resistant to disintegration by water or solvent.
In copending, U.S. Ser. No. 966,422, filed Dec. 4, 1978, assigned to the same assignee to which the present application is assigned, Brodnyan et al. disclose a non-woven fabric, adapted for use as a diaper coverstock, consisting essentially of fibers, at least 50% by weight of the fibers being hydrophobic, and a binder. The binder is a water insoluble hydrophobic copolymer polymerized from 1-8% by weight of a monoethylenically unsaturated carboxylic acid, 50-75% by weight of a C.sub.4 -C.sub.8 alkyl acrylate, and 20-49% by weight of methylmethacrylate, styrene, alpha-methylstyrene or a mixture thereof. The fibers are selected from the group of those produced from polyesters, polyolefins, other vinyl resin fibers and natural fibers. The copolymer-treated fibers are exposed to heat cure conditions, namely, 150.degree. C. for 1.5 min, to effect cure of the binder, "cure" being described as "not normally accompanied by polymer crosslinking." Rather, the application discloses that processes which may be considered to occur in the curing step include wetting of the fibers by the binder and spreading of the binder so as to interlock the fibers.
In copending U.S. Ser. No. 020,689, filed Mar. 15, 1979 and in a copending continuation-in-part application thereof, U.S. Ser. No. 043,998, filed May 31, 1979, both of which are assigned to the same assignee to which the present application is assigned, entitled "Radiation-Curable Allyl Benzoylbenzoate Copolymers, Compositions and Products Thereof, and Methods of Making Them," there is disclosed a film of a linear, essentially uncrosslinked addition copolymer of allyl benzoylbenzoate or benzoyl ring-substituted derivatives thereof such as, for example, allyl-2-(4-methylbenzoyl)benzoate, and at least one other monoethylenically unsaturated monomer wherein the film is carried on or in a substrate adapted to be cured to a crosslinked condition on exposure to UV radiation. The application also discloses the use of the linear addition copolymers containing allyl benzoylbenzoate as binders for non-woven fabrics or webs.